1. Field of the Invention
The present invention relates to a silicon-based film and a photovoltaic element comprising a silicon-based semiconductor layer with at least one pin junction on a support, such as a solar cell, a sensor and the like.
2. Related Background Art
As a method of forming a silicon-based film showing crystallinity, some methods like the cast method in which the film is grown in a liquid phase have been conventionally carried out, but these methods require high temperature processing and have some problems in achieving mass production and low-cost production.
Some methods of forming a silicon-based film showing crystallinity other than the cast method have been disclosed. These methods include a method described in Japanese Patent Application Laid-Open No. 5-109638 in which a polycrystalline silicon film is formed by growing an amorphous silicon film in a solid phase and a method described in Japanese Patent Application Laid-Open No. 5-136062 in which after amorphous silicon film has been formed, hydrogen plasma processing is carried out, and a polycrystalline silicon film is formed by repeating the procedure.
However, in these disclosed methods of forming a silicon-based film showing crystallinity, the former method has the problem that a prolonged heat treatment is needed to crystallize a semiconductor layer with a thickness of several xcexcm or more using a solid phase reaction, and the latter method has the problem of increased processing time due to the repetition of hydrogen plasma processing and the formation of a silicon film.
Furthermore, when a substrate having an uneven surface shape is adopted as a means of increasing the optical confinement effect in a silicon-based film showing an orientation property, especially in a silicon-based film having a columnar structure in the thickness direction, the growth of an orientation plane in the tangential direction of the unevenness in the early stage of the film formation results in the generation of irregular crystal boundaries in the growing process.
Accordingly, an object of the present invention is to provide a silicon-based film which addresses the above described problems. In particular, it is an object of the invention to provide a high-quality silicon-based film that can be formed at a low cost and at a high film forming rate, with a processing time of an industrially acceptable level, especially on a substrate having an uneven surface shape. It is also an object of the invention to provide a photovoltaic element that has such a silicon-based film and is excellent in photoelectric characteristics.
The silicon-based film of the present invention comprises a crystal phase formed on a substrate with a surface shape represented by a function f, wherein the silicon-based film is formed on a substrate with a surface shape having a standard deviation of an inclination arctan (df/dx) from 15xc2x0 to 55xc2x0 within the range of a sampling length dx from 20 nm to 100 nm. A Raman scattering strength resulting from an amorphous component in the silicon-based film is not more than a Raman scattering strength resulting from a crystalline component. A difference between a spacing in a direction parallel to a principal surface of the substrate and a spacing of single crystal silicon is within the range of 0.2% to 1.0% with regard to the spacing of the single crystal silicon.
Further, the present invention provides a silicon-based film that is characterized in that the above described silicon-based film having a crystal phase comprises a crystal of a columnar structure in the thickness direction.
Furthermore, the present invention provides a silicon-based film that is characterized in that the percentage of diffraction strength of (220) plane according to X-ray or electron beam diffraction is 30% or more of the total diffraction strength.
Moreover, the present invention provides a photovoltaic element that is characterized in that in a photovoltaic element comprising a silicon-based semiconductor layer having at least one pin junction on a support, at least one i-type semiconductor layer comprises the above described silicon-based film.
In addition, the present invention provides a photovoltaic element that is characterized in that the above described silicon-based semiconductor layer is formed on a substrate comprising at least a first transparent conductive layer stacked on a support. The first transparent conductive layer has the above described surface shape.
Further, the present invention provides a photovoltaic element that is characterized in that the above described silicon-based film is prepared by a plasma CVD method using a high frequency.
The high frequency is preferably not less than 10 MHz and no more than 10 GHz. The above-described support is preferably a conductive support.